1. Field of the Invention
The present invention relates to a linear motion guide unit having wide application in sliding parts incorporated in, for example, machine tools, assembling machines, testing machines and the like. More particularly, it relates to a mounting construction of a linear motion guide unit in which a slider is movable lengthwise along a track rail.
2. Description of the Prior Art
Conventionally, the linear motion guide units have been known for fundamental means applicable universally in various technical fields. Although the linear motion guide units have been now employed extensively in machinery in various fields such as machine tools, semiconductor manufacturing apparatus, testing instruments, industrial robots and the like, the expansion of uses according to the recently remarkable development in technologies requires more and more such linear motion guide unit to deal with the precision, high-speed moving, easy assemblage, wide applicability and the like.
The linear motion guide unit 60 is in general applied between members, as between a stationary bed and a workpiece table as shown in FIGS. 8 and 9, which are movable relatively to each other. The linear motion guide unit 60 is comprised of a track rail 61 having a pair of lengthwise side surfaces 63 on which are formed raceway grooves 64, and a slider 62 mounted on the track rail 61 for sliding movement along the track rail 61. The track rail 61 is made on the top surface thereof with holes 66 for bolts or screws to fix the track rail 61 to the bed 68.
The slider 62 mainly comprises a casing 70 riding astride the top surface 65 of the track rail 62, end caps 71 attached in abutment against lengthwise opposing ends of the casing 70, each to each end, and end seals 72 arranged on the end caps 71 to seal clearances between the confronting track rail 61 and end caps 71. Both the end caps 71 and end seals 72 are secured to the casing 70 by means of machine screws 73. Bottom seals, not shown, are arranged beneath both the end caps 71 and end seals 72. The casing 70 is provided with raceway grooves 74 confronting the raceway grooves 64 on the track rail 61, and holes 76 bored through a top face 75, into which fit machine screws to mount the casing 70 to the workpiece table 78.
The slider 62 is allowed to move in a sliding manner along the track rail 61 by virtue of rolling elements 81 such as balls, which run through the load areas of raceways 81 defined between the raceway grooves 64 formed on the track rail 61 and the raceway grooves 74 formed in the casing 70. The rolling elements 80 are held in the casing 70 by retainer bands 84 so as to be kept against disassembling even when the slider 62 is separated from the track rail 61. The rolling elements 80 may run through endless circulating paths composed of the load raceways 81, return tunnels 82 bored in the casing 70 to provide non-loaded passages to allow the rolling elements to circulate, and non-loaded turnarounds, not shown, formed in the end caps 71 to interconnect the loaded raceways 81 with their associated non-loaded passages. Moreover, grease nipples 85 to supply lubricant to the endless circulating paths are attached to the end caps 71 and extend outwardly of the end seals 72.
As shown in FIG. 9, the track rail 61 is mounted to the stationary bed 68 by means of bolts 69 that fit into holes 66 in the track rail 61, which is set in place where a bottom surface 86 of the track rail 61 comes in abutment against a seat surface 90 of the bed 68 while the lower area of any one lengthwise side surface 63 comes in abutment against the confronting side edge 91 of the bed 68. In contrast, the slider 62 is attached to a workpiece table 78 with bolts 79 that fit in matching holes 76 in the casing 70. The slider 62 is kept in place with the top face 75 and any one side face 77 thereof being brought into abutment against their confronting bottom surface 92 and a side surface 93 of the workpiece table 78, respectively. In this manner, the side surfaces 77 of the slider 62 are formed on laterally bulged portions 70a to provide sidewise reference surfaces for attachment to the table 78.
Moreover, another prior linear motion guide unit is disclosed in Japanese Patent Laid-Open No. 347009/1992, which comprises a track rail anchored at lengthwise opposing ends thereof, an upper sliding unit riding astride the track rail, and a lower sliding unit depending from the track rail whereby both the upper and lower sliding units are constituted for a linear motion along the track rail.
In addition, Japanese Utility Model Laid-Open No. 193637/1988 discloses linear motion guide means in which a ball-screw drive is combined integrally with a linear guide. Such prior linear motion guide means integral with the ball-screw drive has a tetragon nut mating with a ball-screw drive, a guide rail made with recessed guiding ways where the tetragon nut comes in loose engagement for linear movement along the guide rail, so that rotating the ball screw allows the tetragon nut to move linearly on the guiding ways of the guide rail by virtue of balls that may run through raceways defined between raceway grooves formed on the widthwise opposing side surfaces of the tetragon nut and raceway grooves formed in the guide rail. The linear motion guide means constructed as described just above is plagued with that the tetragon nut occupies a considerable height above the top level of the guide rail.
Disclosed in Japanese Patent Laid-Open No. 298446/1990 is a worktable traveler in which a worktable is supported for linear movement in a guide rail of U-shape in cross section. The worktable is arranged interposed between widthwise opposing inside walls through rolling elements that are allowed to run through raceways of two rows arranged in vertical juxtaposition, which are defined between confronting raceway grooves formed on the side surfaces of the work table and the inside walls of the guide rail. A screw shaft fits in matching hole that is bored in the worktable at a horizontal plane corresponding substantially center lines of vertical distances spanning between the two raceways vertically juxtaposed on the widthwise opposing side surfaces of the worktable. The guide rail is integrally molded so as to provide raceways in which the rolling elements are held in outwardly-opening contact with the confronting raceway grooves of the worktable and the guide rail, that is, phantom lines linking two points of rolling contact of any rolling element with the confronting raceway grooves of the worktable and the guide rail converge towards the center axis of the screw shaft. As an alternative, the guide rail may be made so as to provide another type of raceways in which the rolling elements are held in inwardly-opening contact, where the phantom lines diverge towards the center axis of the screw shaft.
In the prior linear motion guide unit of the type explained above in which the slider of a nut is driven to move linearly in a lengthwise recess in the guide rail by rotating the ball screw, the worktable is mounted to the flat outer surface of the slider with bolts screwed into their matching holes. Nevertheless, it is common that there is provided no reference means for mounting the worktable onto the slider.
For the linear motion guide unit compact in construction in which the slider is moved linearly in the lengthwise recess in the track rail, thus, it has been desirable to mount the worktable to the slider or mount the stationary bed to the track rail at a preselected mounting position and posture and further ensure the mounting position and posture even after a prolonged period of use.